First of all, I want to know what are the Username and password of the fiber optic router. I tried with:

Username: admin
Password: admin

It did not work, I could not login. I tried many more pairs such as, root/admin, Administrator/connect2th and so on.

Wifi name is called SSID. Wifi password is called passkey or passcode. Once you login to the router, you navigate to the "WLAN" tab, you should see SSID and passkey (or passcode). Change them, save/apply and logout.

Do not forget to select encryption type i.e. WPA PSK or WPA2 TKIP.

WLAN may be "Wireless" or some other name depending the model and brand of the router.

Finally, unplug the power of the router, wait for a minute and replug it. You should be able to see the change.